The present invention relates generally to occupant restraint activation sensors, and more specifically to an improved sensor employing optical techniques for sensing the occurrence of a collision in an automotive vehicle, particularly a frontal collision.
Modern automotive vehicles employ passive occupant restraint systems for cushioning or restraining occupant movement when a vehicle is involved in a collision. One type of such restraint system is an inflatable occupant restraint airbag system in which gas is generated to inflate a bag in response to the conditions representative of the occurrence of a collision. In automotive vehicles which utilize airbag systems, the type of collision for which an airbag is deployed is typically a frontal collision. Its occurrence is sensed by a plurality of sensors positioned within the vehicle which detect a deceleration of a predetermined magnitude and duration and thereupon transmit a signal effecting inflation of the airbag. Exemplary of such sensors are those disclosed in U.S. Pat. No. 4,816,627 to Janotik assigned to the assignee of the present invention and U.S. Pat. No. 4,329,549 and U.S. Pat. No. 4,284,863 to Breed. In vehicle occupant restraint systems employing such electromechanical sensors, a sensing mass is positioned for movement generally parallel to the direction of travel of the vehicle. Due to the likelihood of occurrence of angular frontal impacts, which will result in a difference in deceleration levels sensed at positions laterally spaced across the front of the vehicle, it is necessary to provide a plurality of sensors placed in spaced positions to assure the proper sensing of deceleration load indicative of a vehicle collision of sufficient severity to warrant the activation of the airbag system.
An additional quantity of sensors is also used in such systems as a check against inadvertent actuation that might occur in response to short duration, high magnitude deceleration not indicative of a collision.
While this prior art approach to sensing the occurrence of collisions in activating airbag systems has been found to be functionally acceptable, the approach suffers from certain disadvantages. One is the relatively high cost of manufacture attendant the provision of a plurality of discreet sensors for the production of an airbag restraint system, and another is that the prior art systems employing electromechanical acceleration sensors monitor an inherently ambiguous phenomenon, acceleration.